U.S. Pat. No. 4,048,101 to Nakamachi discloses the manufacture of opaque articles having a variegated pattern of streaks. The variegated pattern is produced by extruding a foamed polymeric matrix material together with polymeric accent materials having colorant additives, which form accent color streaks in the polymeric matrix material. The polymeric accent materials have a lower melt index and a larger particle size compared to the foamed matrix material, such that its melt flow rate is lower than that of the matrix material. The accent material and the matrix material are resinous compositions of the same chemical type, to assure bonding therebetween.
U.S. Pat. No. 5,387,381 to Saloom discloses a method for making an opaque capstock having a simulated wood-grain appearance for coextrusion with a polyvinylchloride (PVC) substrate. The capstock material combines a polymeric matrix with accent color pellets consisting essentially of acrylics or polycarbonates having a higher deflection temperature and a larger particle size compared to the polymeric matrix. During an extrusion cycle, the polymeric matrix undergoes melt flow, and the accent color pellets undergo melt flow later in the extrusion cycle, which produces accent color streaks in the extruded capstock matrix.
U.S. Pat. No. 5,866,054 to Dorchester discloses an opaque capstock manufactured with a PVC polymer matrix together with accent color pellets comprised of, acrylic resins blended with poly-α-methyl styrene (PMS) resin. The PMS resin in the pellets has a higher vicat softening point temperature and a higher melt flow index relative to the acrylic resins in the same pellets. Varying the proportion of the PMS to the acrylic resins in the pellets results in a corresponding, soft streaking (gradual color change) or hard streaking (abrupt color change) in the polymer matrix.
US 2005/0003221 A1, to Walrath, discloses an optically clear capstock manufactured from a matrix resin of methacrylic acid polymer or other essentially clear, ultraviolet resistant, matrix materials, and streaker pellets of a polymeric material compatible with the methacrylic matrix resin but having a higher melting point. The matrix resin and streaker pellets are fed into an intake end of an extruder screw feed. The screw feed has four temperature stages, such that the transparent matrix material melts and flows before the streaker pellets become melted within the last temperature stage. Then, the melted materials are extruded to form a transparent capstock having accent color streaks in a transparent matrix. Further, the capstock is coextruded with an underlying polymeric substrate that is visible through the transparent capstock. The capstock has a heat deflection temperature and a glass transition temperature similar to that of the coextruded substrate.
Optically clear polymers have been proposed for making a transparent capstock. Optically clear polymers, such as, polycarbonates and polyacrylates, are highly valued for having a refractive index suitable for use in window panes, lenses and optical coatings. However, an optically clear capstock would be unnecessary, when the capstock is sufficiently non-opaque to an extent that streaks in the capstock are visible through the surface of the capstock. The streaks would be visible in three dimensions to provide an aesthetic three dimensional appearance. Further, an optically clear capstock would be unnecessary, when the capstock is not optically clear, i.e. non-clear, and is sufficiently non-opaque to an extent that a color of a substrate under the capstock would be visible through the surface of the capstock, even when the underlying streaks and underlying substrate themselves are visibly indistinct as the result of being partially obscured by the non-clear, non-opaque capstock.
US 2006/0029775 A1 and 2007/0266562 A1 disclose a capstock or skin material that may be extruded though an extruder, while a core material is coextruded through another extruder. The extrudate is a preliminary shingle shape, a precursor that is compression molded into a final shingle shape as disclosed by US 2006/0029775 A1, U.S. 60/955,051 and PCT/US07/85900, WO2009/0023038, U.S. Ser. No. 11/994,445.